*sigh* I just got finished replacing the three engine mounts on Mater (as my '99 XJ has been dubbed) with new ones from NAPA. One of the front mounts looked pretty shot (the driver's side), but the others might have been ok. Getting the cross-member put back on is a bear! I did a quick test drive and things do seem a bit quieter....

Unfortunately, the noise I had hoped would go away after replacing the mounts is still there. When I accelerate hard (like hard enough to spin the back wheels in 2wd), I hear a grinding. It sounds like something's slipping, and I'm afraid it might be the transfer case (which seems to be leaking, too). Does this sound possible? Is there any troubleshooting I can do to try to isolate the noise and component? I can only reproduce it on the road, not in the garage, unfortunately.

It's got the NP231 t-case, and all three modes work fine. Hard-ish acceleration in 4-hi seems normal (I don't even want to attempt to spin any wheels on even on wet pavement in 4wd). It's just 2-hi.

I also found that the cross-member has a piece broken out by one of the holes which someone attempted to work around by using a washer on the bolt. That bolt is stripped. :-( Gotta find a junk yard!

have you checked you transmission mount? or looked into your differentials? im no master mechanic but i found out recently that my tranny mount was shot causing a grinding type noise under acceleration from a stop, and the clutches in my limited slip were completely worn out making some very uncomfortable noises. just some thoughts.

I actually replaced the tranny mount last night, along with the motor mounts, to no avail. However, as I said above, one of the four cross-member mounting holes is broken, so it's effectively only being held in by 3 bolts. I need to fix that, perhaps before looking elsewhere.

The noise actually seems more noticeable today after changing the mounts (although I had two add'l people in it), but it still doesn't appear unless I'm accelerating fairly hard (but not hard enough to break the tires loose).

I'll experiment a little more tomorrow, maybe see if I can describe it better...

That sounds like a problem I would have!!! At least you fixed some things that needed fixin' anyway!

I bet I've gone through at least one of those on every XJ I've had.

Shocks and motor mounts (and that stupid shroud) are about all I've done maintenance-wise. U-joints and driveshaft bearings are probably next on the list, to get rid of some of the play in the driveline and some really ugly clunking noises when turning at low speeds.